The concentration of n-, respectively, p-charge carriers in semiconductor materials is set by incorporating corresponding doping material elements into the basic crystal lattice. In the conventional processes for fabricating doped semiconductor layers, by way of illustration, VPE, MOCVD, LPE or MBE processes, the concentration of doping material elements in the vicinity of the substrate, on which the layers are produced, is maintained as constant as possible. The doping material element or elements are usually offered in the form of gases, fluids or molecular rays.
In this manner, the constant concentration of doping material elements is set in the solid, i.e. in the produced layer, via the distribution coefficient between the surrounding medium and the solid, thereby setting a constant concentration of charge carriers.
By way of illustration , in order to produce GAInAs layers having a concentration of 10.sup.16 zinc atoms per cm.sup.3, a partial pressure of the zinc compound of approx. 10.sup.-9 bar is needed. On the other hand, setting a doping material concentration of 10.sup.15 cm.sup.-3 requires setting the partial pressure of zinc compounds at a value of less than 10.sup.-10 bar.
As in the conventional processes for producing doped semiconductor layers, the partial pressure of doping material compounds has to be kept constant during the entire production of the layers, producing layers having a low concentration of charge carriers, respectively in the range of 10.sup.15 cm.sup.-3, is technically very elaborate and demanding without any ensurance of actually having set the desired concentration of charge carriers with the necessary precision.
The object of the present invention is to provide a process for producing doped semiconductor layers having a low concentration of charge carriers, which permits producing low concentrations of charge carriers, typically in the range of less than 10.sup.16 cm.sup.-3, with the effort and expense therefor being justifiable.